We are extending our high-resolution X-ray diffraction studies of virus structure and concomitant biochemical experiments on assembly in the following directions: (1) the high-resolution (2.9 A) structure of tomato bushy stunt virus will be refined and extended to 2.5 A; (2) the structure of turnip crinkle virus (TCV) will be determined at 3.0 A and compared with TBSV; (3) the structure of expanded TBSV will be determined at 7.0 A; (4) proteolytic dissection of TCV subunit will be pursued in order to isolate an RNA-binding fragment; (5) initial observations of in vitro reassembly of TCV will be pursued in order to sketch out an assembly pathway consistent with structural details observed in the atomic model.